The field of metal coating concerns processes of applying a protective, decorating, or other type of coating to metal, especially sheet metal. For example, referring to FIG. 1, a sheet 20 of metal may be used to form metal products such as can ends and bottle caps. Coating material, such as gold sanitary enamel is applied to the planar face 21 of sheet metal 20 for hygienic or aesthetic reasons. If one peers inside an aluminum beverage can, for example, one can see the sheen of this type of coating material. As shown in FIG. 1, sheet metal 20 is stamped into desired articles 22 (in this case, can ends). This results in a pattern of waste or scrap areas 24 between the desired articles 22. Because coating is expensive, it is desirable to avoid coating scrap areas 24. Other areas where coating is not desired may exist, for example, at portions of sheet metal 20 that are intended to become can seams.
The metal decorating industry has tried for many years to avoid coating scrap and other areas. A typical coating device used to achieve this objective includes a composition roller, a scrapper or chill roller, a fountain roller, and a distributor roller. These rollers are rotably mounted in parallel, adjacent relation, with the fountain roller engaging the distributor roller, and the distributor roller engaging the composition roller. A material feed supplies coating material to the fountain roller. As the rollers rotate, coating material is applied in sequence from the fountain roller to the distributor roller, and then to the engaging the composition roller. A material feed supplies coating material to the fountain roller. As the rollers rotate, coating material is applied in sequence from the fountain roller to the distributor roller, and then to the composition roller. Sheet metal 20 is fed between the composition roller and the scrapple roller by a conveying mechanism. It is the composition roller that actually applies the coating to sheet metal 20.
In accordance with an existing technique, sections are engraved out of the composition roller in a pattern corresponding to the pattern of scrap areas 24. The portions of the composition roller which are engraved carry no coating material, and, therefore apply no coating to the scrap areas 24 of sheet metal 20.
The existing technique has a number of drawbacks. Engraving cut-out sections in the composition roller is a time consuming and costly process. Because the cut-out sections are engraved onto a cylindrical roller (as opposed to a flat surface), accurate cuts are difficult to obtain and many rollers are spoiled in the attempt.
To ease the engraving process, rubber rollers have been used, but materials like rubber wear poorly. Further, the composition roller must be changed each time a new job is run through the coating apparatus. This, too, is a labor intensive process. Another drawback with using rubber rollers is that rubber tends to retain the coating material. This requires the composition roller to be applied to sheet metal 20 with high pressure. To provide sufficient pressure, the rubber composition roller is in direct contact with the scrapple roller. As sheet metal 20 is sandwiched between the composition roller and the scrapple roller, the thickness of sheet metal 20 causes the rubber composition roller to be compressed against the face of sheet metal 20, thus providing the pressure required to release the coating material from the composition roller. Once sheet metal 20 has passed through the coating apparatus, the composition roller directly contacts the scrapple roller. As a result, coating material is transferred from the composition roller to the scrapple roller. This is undesirable, and requires labor-intensive cleaning to remove the coating material from the scrapple roller. In addition, the agents used to clean the scrapple roller include solvents which raise issues of occupational safety and environmental pollution. Ideally, a composition roller would not require substantial pressure to impart coating to sheet metal 20, and therefore would not be in direct contact with the scrapple rollers.